Chapter 24

1. Chapter 24 The Origin of Species

2. Figure 24.1 • Overview: The “Mystery of Mysteries” • Darwin explored the Galápagos Islands • And discovered plants and animals found nowhere else on Earth

3. The origin of new species, or speciation • Is at the focal point of evolutionary theory, because the appearance of new species is the source of biological diversity • Evolutionary theory • Must explain how new species originate in addition to how populations evolve • Macroevolution • Refers to evolutionary change above the species level

4. (b) Cladogenesis (a) Anagenesis Figure 24.2 • Two basic patterns of evolutionary change can be distinguished • Anagenesis • Cladogenesis

5. Concept 24.1: The biological species concept emphasizes reproductive isolation • Species • Is a Latin word meaning “kind” or “appearance”

6. The Biological Species Concept • The biological species concept • Defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but are unable to produce viable fertile offspring with members of other populations

7. Similarity between different species. The eastern meadowlark (Sturnella magna, left) and the western meadowlark (Sturnella neglecta, right) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild. (a) (b) Diversity within a species. As diverse as we may be in appearance, all humans belong to a single biological species (Homo sapiens), defined by our capacity to interbreed. Figure 24.3 A, B

8. Reproductive Isolation • Reproductive isolation • Is the existence of biological factors that impede members of two species from producing viable, fertile hybrids • Is a combination of various reproductive barriers

9. Prezygotic barriers • Impede mating between species or hinder the fertilization of ova if members of different species attempt to mate • Postzygotic barriers • Often prevent the hybrid zygote from developing into a viable, fertile adult

10. Prezygotic barriers impede mating or hinder fertilization if mating does occur Behavioral isolation Habitat isolation Temporal isolation Mechanical isolation Individualsof differentspecies Matingattempt HABITAT ISOLATION MECHANICAL ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION (g) (b) (d) (e) (f) (a) (c) Figure 24.4 • Prezygotic and postzygotic barriers

11. Gameticisolation Reducehybridfertility Reducehybridviability Hybridbreakdown Viablefertileoffspring Fertilization REDUCED HYBRID VIABILITY GAMETIC ISOLATION HYBRID BREAKDOWN REDUCED HYBRID FERTILITY (k) (j) (m) (l) (i) (h)

12. (a) (b) Sympatric speciation. A smallpopulation becomes a new specieswithout geographic separation. Allopatric speciation. A population forms a new species while geographically isolated from its parent population. Figure 24.5 A, B • Concept 24.2: Speciation can take place with or without geographic separation • Speciation can occur in two ways • Allopatric speciation • Sympatric speciation

13. Allopatric (“Other Country”) Speciation • In allopatric speciation • Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations

14. A. harrisi A. leucurus Figure 24.6 • Once geographic separation has occurred • One or both populations may undergo evolutionary change during the period of separation

15. Sympatric (“Same Country”) Speciation • In sympatric speciation • Speciation takes place in geographically overlapping populations

16. Habitat Differentiation and Sexual Selection • Sympatric speciation • Can also result from the appearance of new ecological niches

17. Allopatric and Sympatric Speciation: A Summary • In allopatric speciation • A new species forms while geographically isolated from its parent population • In sympatric speciation • The emergence of a reproductive barrier isolates a subset of a population without geographic separation from the parent species

18. Figure 24.11 Adaptive Radiation • Adaptive radiation • Is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities

19. N 1.3 million years Dubautia laxa MOLOKA'I KAUA'I MAUI 5.1 million years Argyroxiphium sandwicense O'AHU LANAI 3.7 million years HAWAI'I 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis Figure 24.12 • The Hawaiian archipelago • Is one of the world’s great showcases of adaptive radiation

20. Studying the Genetics of Speciation • The explosion of genomics • Is enabling researchers to identify specific genes involved in some cases of speciation

21. The Tempo of Speciation • The fossil record • Includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then apparently disappear • Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe these periods of apparent stasis punctuated by sudden change

22. Time (b) (a) Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations. Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence. Figure 24.13 • The punctuated equilibrium model • Contrasts with a model of gradual change throughout a species’ existence